Method for producing a piston

Abstract

A method is disclosed for producing a piston (8) having a circumferential seal in the form of a circular cup seal (16). In a functional, installed state, the cup seal (16) has a profile consisting of a leg held in the piston (8) and aligned radially with respect to the piston longitudinal axis (19) in a radial region (17) and of a leg which is bent by approximately 90° into an axial region (18) and is aligned approximately parallel to the piston longitudinal axis (19). The cup seal (16) is mounted in a mold as a flat or arched preform (21, 21a) with a radial region (17a, 17b) which forms the approximately radial leg, aligned with the piston longitudinal axis (19). A circumferential region (18a, 18b) projecting radially beyond the mold cavity is shaped into the axial region (18) after removing the piston from the mold to obtain the functional contour of the installed state of the cup seal (16).

The invention claimed is: 
     
       1. A method for producing a piston having a central piston longitudinal axis and a piston circumference and having a circumferential seal in the form of a circular cup seal having a functional contour in an installed state, the functional contour having a first leg formed by a radial region held in the piston and radially centered around the central piston longitudinal axis and of a second leg formed by an axial region bent by approximately 90° with respect to the radial region and aligned approximately parallel to the central piston longitudinal axis, the method comprising the following steps:
 placing a cup seal into a mold having a mold cavity for molding the piston in a first step in such a way that the radial region projects into the mold cavity and is radially centered in the mold cavity and that the axial region is held by the mold in a shape of a circumferential region that differs from the shape of the axial region of the functional contour, 
 overmolding only the radial region projecting into the mold cavity in a second step by filling the mold cavity with piston material to form the piston including the overmolded cup seal, 
 removing the piston including the overmolded cup seal from the mold in a third step, and 
 after the step of removing the piston, changing the shape of the circumferential region of the overmolded cup seal into the shape of the axial region of the functional contour of the overmolded cup seal corresponding to the installed state. 
 
     
     
       2. The method as claimed in  claim 1 , wherein, prior to being placed in the mold, the cup seal is a flat or arched preform with the radial region projecting into the mold cavity and with the circumferential region projecting radially beyond the mold cavity, the circumferential region being formed into the axial region in the fourth step, wherein the fourth step is carried out by permanently shaping the circumferential region into the second leg, bent by approximately 90° with respect to the radial region, to obtain the functional contour of the installed state. 
     
     
       3. The method as claimed in  claim 2 , wherein the fourth step of shaping the circumferential region of the preform into the axial region of the functional contour of the overmolded cup seal is performed by cold or hot forming with a sizing tool surrounding the circumferential region of the preform. 
     
     
       4. The method as claimed in  claim 3 , wherein the sizing tool has an annular shape and has an inside diameter corresponding approximately to an outside diameter of the axial region of the overmolded cup seal forming the second leg to shape the circumferential region of the preform into the axial region, and wherein the sizing tool is moved in an axial direction relative to the piston, over the radially projecting circumferential region of the preform while surrounding the piston circumference. 
     
     
       5. The method as claimed in  claim 3 , wherein the sizing tool is a cylinder of a reciprocating piston machine, and wherein the step of shaping the radially projecting circumferential region of the preform into the axial region of the functional contour of the overmolded cup seal is brought about by pushing the piston with the preform mounted thereon into the cylinder. 
     
     
       6. The method as claimed in  claim 1 , wherein the cup seal, prior to being placed in the mold, has the functional contour and wherein the fourth step is carried out by allowing the circumferential region to return elastically to the functional contour to form the second leg. 
     
     
       7. The method as claimed in  claim 6 , wherein, in the first step, the axial region of the cup seal is bent open into an approximately radial direction and substantially in alignment with the radial region when the axial region is introduced into the mold and is surrounded by the mold. 
     
     
       8. The method as claimed in  claim 6 , wherein, in the first step, the axial region of the cup seal is overbent radially when the axial region is introduced into the mold and is surrounded by the mold. 
     
     
       9. The method as claimed in  claim 1 , wherein the piston is a pendulum piston integral with a connecting rod having a connecting rod shank and a connecting rod eye with a bearing bore at an end of the connecting rod shank opposite from the piston. 
     
     
       10. The method as claimed in  claim 7 , wherein the piston is injection-molded in a mold from one plastic material and in one piece with the connecting rod shank and the connecting rod eye. 
     
     
       11. The method as claimed in  claim 10 , wherein the mold is a three-part mold, of which two mold halves are divided in a transverse plane extending centrally through the piston, through the connecting rod shank, and through the connecting rod eye, and wherein a third mold part adjoins the mold halves in a parting plane extending perpendicular to the central piston longitudinal axis, wherein the parting plane for the third mold part is arranged in in an axial section adjoining the clamped radial region of the cup seal, the mold having closing and opening movements of the two mold halves that occur perpendicularly to the piston longitudinal axis and the third mold part having closing and opening movements that occur in the direction of the piston longitudinal axis, and the circumferential regions of the cup seal or of the preform are accommodated in recesses in at least one part of the three-part mold when the mold is closed. 
     
     
       12. The method as claimed in  claim 10 , wherein the mold is an at least two-part mold, of which two mold halves are divided in a transverse plane extending centrally through the piston and the connecting rod shank, and wherein the axial region, bent by approximately 90°, of the cup seal is accommodated in recesses in the two mold halves when the mold is closed, said recesses being dimensioned in such a way that they overbend the axial region, bent by approximately 90°, of the cup seal in the direction of the piston longitudinal axis, and wherein the opening movement of the two mold halves takes place perpendicularly to the piston longitudinal axis. 
     
     
       13. The method as claimed in  claim 1 , wherein the radial region of the cup seal has apertures and/or dovetail cutouts for location in the piston, said apertures and/or cutouts being filled by the piston material during the production of the piston. 
     
     
       14. The method as claimed in  claim 1 , wherein the radial region of the cup seal has at least one annular groove or at least one projection for sealing with respect to the piston. 
     
     
       15. The method as claimed in  claim 1 , wherein the piston is a piston of a reciprocating piston machine. 
     
     
       16. The method as claimed in  claim 15 , wherein the reciprocating piston machine is a compressor.